1. Field of the Invention
The present invention relates to a fuel injection control device for an internal combustion engine. More particularly, it relates to such a device whereby a fuel injection is controlled by detecting a degree of opening of the throttle.
2. Description of the Related Art
The use of electric fuel injectors to supply fuel to the engine is wide-spread, and many fuel injection control devices have been proposed for a precise control of the supply of the fuel in response to the engine operating conditions, to obtain an optimum performance by the engine. These fuel injection control devices can be generally classified into the following types: The type in which the degree of opening of the throttle valve which regulates the flow of the intake air in the engine, and the revolution speed of the engine, is detected, to estimate the amount of fuel to be injected into the engine (c.f., for example, Japanese Unexamined Patent Publication (Kokai) Nos. 59-28031 and 60-122237); the type in which the actual volume of the intake air is detected instead of the above throttle opening; and the type in which the intake air pressure is detected.
The above three types of fuel injection control devices have advantageous control characteristics, respectively. However, it is clear that the fuel injection control device of the first type obtains the quickest response, because the flow of the intake air is controlled by changing the degree of opening of the throttle valve, to bring the operating condition of the engine to a desired condition. Namely, the response in the case of the second and the third types is delayed in comparison to that of the first type, since the above second and third types detect the volume and the pressure of the intake air, respectively, as a control parameter for the engine load, which phenomena are caused by a change in the degree of opening of the throttle, and since there may be a delay in the response of the air flow meter and pressure sensor when detecting these parameters.
Nevertheless, an injection control device in which the amount of the fuel to be injected in the engine is determined by detecting the degree of opening of the throttle valve and the revolution speed of the engine is not without problems.
Fundamentally, the amount of fuel required by the engine should be decided in correspondence with the flow of the intake air and the revolution speed of the engine, and in the case of the first type of fuel injection control device, the degree of opening of the throttle valve is used as a parameter for estimating the flow of the intake air. If the degree of opening of the throttle valve completely corresponds to the flow of the intake air, the above estimation will accurately represent the actual flow of the intake air, and the decision on the amount of fuel required will rapidly follow and maintain correspondence with the amount of fuel required to establish a good response.
However, the relationship between the degree of opening of the throttle valve and the actual flow of the intake air cannot be assumed to be always in complete correspondence, since some engines are provided with idle speed control devices comprising a bypass air passage with bypasses the throttle valve, for controlling the idle speed and warming up operation of the engine by changing the flow area of the bypass air passage. Also, some air leakage will flow into the intake air passage without passing through the throttle valve, or the volumetric efficiency will change due to a change of back pressure or in the intake valve characteristic after a long period of use. Also, in the detecting means for detecting the degree of opening of the throttle valve, detecting errors may occur in the sensor itself and execution errors may occur in an analog and digital converter or the like as a signal handling means for handling the sensor output, with the result that the accuracy of the detection of the degree of opening of the throttle valve will be limited to a certain extent.
Therefore, it can be considered that the fuel injection control device in which the amount of fuel to be injected is calculated by using the degree of opening of the throttle valve, on one hand, will provide a good control response, but on the other hand, will have a poor control accuracy in comparison to the other types of fuel injection control devices, and thus a problem arises in that such a fuel injection control device cannot be used in an internal combustion engine in which a good fuel economy and emission rate must be realized by controlling the air fuel ratio.
To solve this problem, the above-mentioned Japanese Unexamined Patent Publications (Kokai) No. 59-28031 proposed that the idle speed and warming up control be effected by control of the degree of opening of the throttle valve, instead of by control of the bypass passage, thus shutting off all of the bypass air flow. However, this raises a further problem of providing a complex throttle valve operating mechanism which, nevertheless, cannot precisely control the idle speed.